"""
Modbus Modicon Payload Builder
-----------------------------------------------------------

This is an example of building a custom payload builder
that can be used in the pymodbus library. Below is a 
simple modicon encoded builder and decoder.
"""
from struct import pack, unpack
from pymodbus.constants import Endian
from pymodbus.interfaces import IPayloadBuilder
from pymodbus.utilities import pack_bitstring
from pymodbus.utilities import unpack_bitstring
from pymodbus.exceptions import ParameterException


class ModiconPayloadBuilder(IPayloadBuilder):
    """
    A utility that helps build modicon encoded payload
    messages to be written with the various modbus messages.
    example::

        builder = ModiconPayloadBuilder()
        builder.add_8bit_uint(1)
        builder.add_16bit_uint(2)
        payload = builder.build()
    """

    def __init__(self, payload=None, endian=Endian.Little):
        """ Initialize a new instance of the payload builder

        :param payload: Raw payload data to initialize with
        :param endian: The endianess of the payload
        """
        self._payload = payload or []
        self._endian = endian

    def __str__(self):
        """ Return the payload buffer as a string

        :returns: The payload buffer as a string
        """
        return ''.join(self._payload)

    def reset(self):
        """ Reset the payload buffer
        """
        self._payload = []

    def build(self):
        """ Return the payload buffer as a list

        This list is two bytes per element and can
        thus be treated as a list of registers.

        :returns: The payload buffer as a list
        """
        string = str(self)
        length = len(string)
        string = string + ('\x00' * (length % 2))
        return [string[i:i+2] for i in range(0, length, 2)]

    def add_bits(self, values):
        """ Adds a collection of bits to be encoded

        If these are less than a multiple of eight,
        they will be left padded with 0 bits to make
        it so.

        :param values: The value to add to the buffer
        """
        value = pack_bitstring(values)
        self._payload.append(value)

    def add_8bit_uint(self, value):
        """ Adds a 8 bit unsigned int to the buffer

        :param value: The value to add to the buffer
        """
        fstring = self._endian + 'B'
        self._payload.append(pack(fstring, value))

    def add_16bit_uint(self, value):
        """ Adds a 16 bit unsigned int to the buffer

        :param value: The value to add to the buffer
        """
        fstring = self._endian + 'H'
        self._payload.append(pack(fstring, value))

    def add_32bit_uint(self, value):
        """ Adds a 32 bit unsigned int to the buffer

        :param value: The value to add to the buffer
        """
        fstring = self._endian + 'I'
        handle = pack(fstring, value)
        handle = handle[2:] + handle[:2]
        self._payload.append(handle)

    def add_8bit_int(self, value):
        """ Adds a 8 bit signed int to the buffer

        :param value: The value to add to the buffer
        """
        fstring = self._endian + 'b'
        self._payload.append(pack(fstring, value))

    def add_16bit_int(self, value):
        """ Adds a 16 bit signed int to the buffer

        :param value: The value to add to the buffer
        """
        fstring = self._endian + 'h'
        self._payload.append(pack(fstring, value))

    def add_32bit_int(self, value):
        """ Adds a 32 bit signed int to the buffer

        :param value: The value to add to the buffer
        """
        fstring = self._endian + 'i'
        handle = pack(fstring, value)
        handle = handle[2:] + handle[:2]
        self._payload.append(handle)

    def add_32bit_float(self, value):
        """ Adds a 32 bit float to the buffer

        :param value: The value to add to the buffer
        """
        fstring = self._endian + 'f'
        handle = pack(fstring, value)
        handle = handle[2:] + handle[:2]
        self._payload.append(handle)

    def add_string(self, value):
        """ Adds a string to the buffer

        :param value: The value to add to the buffer
        """
        fstring = self._endian + 's'
        for c in value:
            self._payload.append(pack(fstring, c))


class ModiconPayloadDecoder(object):
    """
    A utility that helps decode modicon encoded payload
    messages from a modbus reponse message. What follows is
    a simple example::

        decoder = ModiconPayloadDecoder(payload)
        first   = decoder.decode_8bit_uint()
        second  = decoder.decode_16bit_uint()
    """

    def __init__(self, payload, endian):

        """ Initialize a new payload decoder

        :param payload: The payload to decode with
        """
        self._payload = payload
        self._pointer = 0x00
        self._endian = endian

    @staticmethod
    def from_registers(registers, endian=Endian.Little):
        """ Initialize a payload decoder with the result of
        reading a collection of registers from a modbus device.

        The registers are treated as a list of 2 byte values.
        We have to do this because of how the data has already
        been decoded by the rest of the library.

        :param registers: The register results to initialize with
        :param endian: The endianess of the payload
        :returns: An initialized PayloadDecoder
        """
        if isinstance(registers, list): # repack into flat binary
            payload = ''.join(pack('>H', x) for x in registers)
            return ModiconPayloadDecoder(payload, endian)
        raise ParameterException('Invalid collection of registers supplied')

    @staticmethod
    def from_coils(coils, endian=Endian.Little):
        """ Initialize a payload decoder with the result of
        reading a collection of coils from a modbus device.

        The coils are treated as a list of bit(boolean) values.

        :param coils: The coil results to initialize with
        :param endian: The endianess of the payload
        :returns: An initialized PayloadDecoder
        """
        if isinstance(coils, list):
            payload = pack_bitstring(coils)
            return ModiconPayloadDecoder(payload, endian)
        raise ParameterException('Invalid collection of coils supplied')

    def reset(self):
        """ Reset the decoder pointer back to the start
        """
        self._pointer = 0x00

    def decode_8bit_uint(self):
        """ Decodes a 8 bit unsigned int from the buffer
        """
        self._pointer += 1
        fstring = self._endian + 'B'
        handle = self._payload[self._pointer - 1:self._pointer]
        return unpack(fstring, handle)[0]

    def decode_16bit_uint(self):
        """ Decodes a 16 bit unsigned int from the buffer
        """
        self._pointer += 2
        fstring = self._endian + 'H'
        handle = self._payload[self._pointer - 2:self._pointer]
        return unpack(fstring, handle)[0]

    def decode_32bit_uint(self):
        """ Decodes a 32 bit unsigned int from the buffer
        """
        self._pointer += 4
        fstring = self._endian + 'I'
        handle = self._payload[self._pointer - 4:self._pointer]
        handle = handle[2:] + handle[:2]
        return unpack(fstring, handle)[0]

    def decode_8bit_int(self):
        """ Decodes a 8 bit signed int from the buffer
        """
        self._pointer += 1
        fstring = self._endian + 'b'
        handle = self._payload[self._pointer - 1:self._pointer]
        return unpack(fstring, handle)[0]

    def decode_16bit_int(self):
        """ Decodes a 16 bit signed int from the buffer
        """
        self._pointer += 2
        fstring = self._endian + 'h'
        handle = self._payload[self._pointer - 2:self._pointer]
        return unpack(fstring, handle)[0]

    def decode_32bit_int(self):
        """ Decodes a 32 bit signed int from the buffer
        """
        self._pointer += 4
        fstring = self._endian + 'i'
        handle = self._payload[self._pointer - 4:self._pointer]
        handle = handle[2:] + handle[:2]
        return unpack(fstring, handle)[0]

    def decode_32bit_float(self, size=1):
        """ Decodes a float from the buffer
        """
        self._pointer += 4
        fstring = self._endian + 'f'
        handle = self._payload[self._pointer - 4:self._pointer]
        handle = handle[2:] + handle[:2]
        return unpack(fstring, handle)[0]

    def decode_bits(self):
        """ Decodes a byte worth of bits from the buffer
        """
        self._pointer += 1
        handle = self._payload[self._pointer - 1:self._pointer]
        return unpack_bitstring(handle)

    def decode_string(self, size=1):
        """ Decodes a string from the buffer

        :param size: The size of the string to decode
        """
        self._pointer += size
        return self._payload[self._pointer - size:self._pointer]


# -------------------------------------------------------------------------- #
# Exported Identifiers
# -------------------------------------------------------------------------- #
__all__ = ["ModiconPayloadBuilder", "ModiconPayloadDecoder"]
